A spirometer is described and, more particularly, a portable spirometer having multiple concentric air flow tubes for use in detecting and diagnosing pulmonary disorders and including a wireless connection to a mobile device for transferring data to other computers for remote monitoring patient lung function and performance.
A spirometer is a device that monitors respiration by measuring the amount of air inhaled and exhaled by a patient for a period of time. Many conventional spirometers evaluate air flow by measuring the pressure difference across an obstruction placed in the flow channel at an intermediate portion of the spirometer. A differential pressure sensor is connected to two outlets from the flow channel on either side of the flow obstruction. The obstruction can be comprised by a variety of means including a restriction in the flow channel or a fine wire mesh or ceramic screen. The sensor signal as a differential pressure is then converted into a voltage as electronic data, which can be displayed on a monitor, transmitted to a computer, or shared with others.
Spirometers are used for the diagnosis of pulmonary diseases. Spirometers are also used as a part of pulmonary function testing and to evaluate lung function in people with obstructive or restrictive lung disease, such as asthma, emphysema, chronic obstructive pulmonary disease (COPD) or other airway disorders or conditions relating to the respiratory system. For example, asthma can cause chronic or acute symptoms that can range from annoying to life threatening. These symptoms typically range from coughing, wheezing, and shortness of breath to drastically decreased air exchange as measured by a spirometer.
Determining lung function uses various types of spirometric examinations in which the vital capacity and forced expiratory volume at predetermined intervals are measured for comparison with expected values. Evaluation of lung function is through comparison of the subject's vital capacity with theoretical values which are dictated by the sex, age and height of the subject. A number of criteria are used for determining the condition of the patient. Two often used criteria are forced vital capacity (FVC) of the patient's lungs and the forced expiratory volume timed for one second (FEV1). The ratio of these two volumes (FEV1/FVC) is also used for diagnostic purposes. In normal patients the ratio of FEV1/FVC is greater than 75% (0.75). A ratio of less than 75% is indicative of an obstructive impairment, such as asthma or emphysema.
Spirometers can also measure key parameters that are precursor symptoms of asthma, such as peak respiratory flow or peak expiratory flow (PEF), which is defined as the maximum flow rate recorded during a forced expiration of air from the lungs. Respiratory conditions can be monitored by measuring peak flow with a portable spirometer. Peak expiratory airflow, as well as other lung function measurements, can be used to identify problems before they become apparent to the patient. With careful monitoring of these values, it may be possible to help the patient recognize impending problems and avert an emergency or lessen its severity.
Spirometers are also used to study the progress of lung performance to assist in the treatment of a variety of airway disorders, diseases and conditions. Remotely monitoring a treatment plan put in place with a healthcare provider helps maintain adherence to the treatment plan by the patient and can additionally include tracking medication usage for review by the healthcare provider. For example, pulmonologists overseeing asthma patients recommend that patients with moderate to severe asthma should record their peak expiratory flow on a daily basis to determine the effectiveness of the treatment given to them. It is also important to know whether a patient is administering medication according to the treatment plan. Therefore, a need exists for methods and systems that track a patient's physiological parameters (e.g., peak expiratory airflow in asthma, FEV1 in COPD, FVC in IPF, etc.) and medication administration on a continual basis, rather than be limited to periodic visits by the patient to their healthcare provider to help manage their respiratory diseases acutely and/or chronically.
Conventional spirometers also have some disadvantages, including an inability of some designs to equally and accurately measure flow across the full dynamic range of flow rates or to laminarize high flow rates well. Moreover, designs that approach this linear transduction are often plagued by high cost or physically large size, precluding the opportunity for individuals to purchase or carry them around for use when they may be most needed. From a human factors standpoint, other device designs suffer from the inclusion of moving parts or poorly accessible parts that can impact cleaning, device sanitation, and ultimately reduce measurement accuracy from wear-and-tear and clogging. Additionally, many of these conventional desktop spirometers cannot be converted to smaller form factors because of induced turbulence caused by passing very high flow rates (up to 840 liters/minute) through narrow passageways that comply with average mouth sizes (scale of centimeters). Mathematically, this turbulence can be modeled by the Reynolds number of the fluid, which will exceed a critical level under conditions of high volumetric flow rate, large hydraulic diameter, and small cross-section area, resulting in a fluid flow that has eddies and non-uniform flow distributions. In turbulent flow, local velocities and pressures of fluid fluctuate irregularly and in a random manner, which can create deviance in the flow rate measurement that only grows during volumetric integration, eventually approaching or exceeding allowable error.
For the foregoing reasons, there is a need for a portable, low-cost, durable spirometer and method that provides reliable results via laminarization of flow across a wide dynamic range of flow rates for measuring and monitoring lung function. In some cases, such a device could tremendously benefit patient health for chronic lung conditions such as asthma, COPD, cystic fibrosis, IPF, and so forth; in other cases, such a device could be used to digitally deliver remote pulmonary rehabilitation trials that have been traditionally performed in cardiopulmonary rehabilitation centers or hospitals; in still other cases; such a device could enable new forms of digital clinical trials that track and aggregate granular lung function data for phase I through phase IV trials. Thus, such a spirometer should be sufficiently easy to use for individuals themselves to perform remote monitoring of their lung function. The spirometer should also be capable of interfacing with a mobile device or a desktop computer or the internet to allow convenient data collection and transfer so that healthcare professionals, clinical trial coordinators, and any other privileged individual can check the reliability of the results and implementation and monitoring of a treatment plan, study protocol, rehabilitation plan, and so forth.